Stabilizer and rotary expansible drill bit apparatus

ABSTRACT

The upper end of a rotary drill bit having initially retracted expansible cutters is connected to a stabilizer having initially retracted expansible stabilizer members, the upper end of the stabilizer being connectable to a rotary drill pipe string. The apparatus is lowered in a bore hole on the drilling string and rotated, the cutters being expanded to cut into the bore hole and enlarge it to a desired diameter, the apparatus being lowered to progressively continue enlarging the hole in a downward direction. Upon the stabilizer moving into the enlarged hole, its stabilizer members are expanded laterally to an extent conforming to the enlarged hole diameter, being engageable with the wall of the bore hole to stabilize the bit therebelow.

The present invention relates to the stabilization of drill bits for usein drilling bore holes, and more specifically to stabilizer apparatusfor enlarging bore holes produced by drill bits having expandablecutters. The stabilizer portion of the apparatus functions in theenlarged portion of the bore hole to center the expanded cutters of anexpandable bit during lengthwise drilling of the enlarged diameter borehole.

As disclosed in U.S. Pat. No. 2,699,921, a rotary drill bit hasexpansible cutters thereon adapted to enlarge the diameter of a borehole. Below this bit a stabilizer device is provided which hasstabilizing arms expandable outwardly into engagement with the wall of apilot hole below and of a much smaller diameter than the enlarged holebeing produced by the expansible type of bit. The stabilization that canbe effected by such a bit and stabilizer combination is rather limited,primarily because of the small diameter bore hole in which thestabilizer itself is operating, which is substantially less than thediameter of the enlarged hole being produced by the drill bitthereabove.

Stabilizers are known having fixed blades or ribs which can effect theirstabilization function in a hole of a predetermined diameter thatconforms to the effective diameter of the stabilizing members on thestabilizer itself. It is evident, however, that such a fixed blade orrib stabilizer can have no stabilizing function when introduced into abore hole of substantially larger diameter than the effective diameterof the stabilizer itself.

In accordance with the present invention, apparatus is provided which iscapable of stabilizing a rotary expansible drill bit within an enlargedbore hole being produced by the expanded bit cutters. The stabilizeremploys expansible stabilizer arms, blades, or ribs which are positionedabove the expanded cutters of the drill bit. The stabilizer is capableof moving through a smaller diameter hole or casing, its stabilizerarms, blades, or ribs then being expandable outwardly into engagementwith the wall of the enlarged hole produced by the expansible type ofbit mounted in the bore hole below the stabilizer unit. The stabilizerarms have an effective diameter conforming closely to the diameter ofthe enlarged hole and can bear against the wall of the enlarged hole toan effective extent, to maintain the expansible drill bit coaxial withthe original bore hole that the expansible cutters are enlarging,resisting the tendency of the expanded cutters of the bit to drill amisaligned or deviated enlarged hole.

An object of the invention is to provide a stabilizer having arms, ribs,blades or the like that are expandable outwardly from a retractedposition to an expanded position for operating in an enlarged hole forthe purpose of effecting stabilization of an expansible bit in theenlarged hole.

A further object of the invention is to provide a combination of anexpansible drill bit capable of enlarging a bore hole and of astabilizer having expansible arms thereon adapted to coact with the wallof the enlarged hole for the purpose of stabilizing the bit within thehole.

This invention possesses many other advantages, and has other purposeswhich may be made more clearly apparent from a consideration of a formin which it may be embodied. This form is shown in the drawingsaccompanying and forming part of the present specification. It will nowbe described in detail, for the purpose of illustrating the generalprinciples of the invention; but it is to be understood that suchdetailed description is not to be taken in a limiting sense.

Referring to the drawings:

FIGS. 1a and 1b together constitute a longitudinal section taken alongthe line 1--1 of FIG. 4, through a combination of an upper stabilizerportion of an apparatus and a lower expansible drill bit portion, thearms of the stabilizer and the cutters of the drill bit both being intheir initial retracted position for movement through a well casinglocated within a previously drilled bore hole, which bore hole extendsbelow the lower end or shoe of the casing, FIG. 1b being a lowercontinuation of FIG. 1a.

FIGS. 2a and 2b are quarter longitudinal sections corresponding to FIGS.1a and 1b, respectively, disclosing the cutters of the expansible bitexpanded outwardly to their maximum position to drill an enlarged hole,while the arms of the stabilizer have been expanded to a slight extentonly to bear against the wall of the well casing or of the previouslydrilled pilot hole, FIG. 2b being a lower continuation of FIG. 2a.

FIGS. 3a and 3b are longitudinal sections conforming to FIGS. 2a and 2b,respectively, disclosing both the cutters of the expansible drill bitand the arms of the stabilizer expanded outwardly to their fullestextents, FIG. 3b being a lower continuation of FIG. 3a.

FIG. 4 is a cross-section taken along the line 4--4 on FIG. 1a;

FIG. 5 is a cross-section taken along the line 5--5 of FIG. 1a; and

FIG. 6 is a cross-section taken along the line 6--6 of FIG. 1b.

As illustrated in the drawings, a well bore or other bore hole has beendrilled through a formation to a predetermined diameter slightly lessthan the inside diameter of a string of well casing 10, 11 previouslyinstalled in the hole. It is desired to enlarge the diameter of the borehole 200 through use of an expansible drill bit 15 which may be of anyknown type, such as illustrated in U.S. Pat. No. 3,101,124, and tostabilize the bit in the enlarged well bore through use of an expansibletype of stabilizer connected to the drill bit directly or indirectly,the stabilizer itself being secured to the lower end of a string ofdrill pipe 13 extending to the top of the well bore and rotated throughthe usual rotary table or the like. (not shown)

The drill bit includes a mandrel 60 having an upper pin 61 threadedlyconnected to the lower end of the tubular main body 14 of thestabilizer. If desired, intervening drill pipe or drill collars (notshown) can be secured to and between the stabilizer and the drill bit. Akelly or mandrel 39 is also slidably splined to this body 14 by virtueof the non-circular exterior 39a of a portion 42 of the kelly beingdisposed within a companion non-circular bore 14a in the body of thetool. The non-circular kelly exterior 39a and bore 14a can be achievedin any suitable manner. As disclosed, a pair of opposed shoes 43, 44 aremounted in the body bore or socket and suitably welded thereto, the flatfaces of these shoes engaging companion opposed flat surfaces on theexterior of the kelly or mandrel (FIG. 5). The kelly extends upwardlyfrom the body and has a threaded pin threadedly attached to the lowerend of the string of drill pipe 13 extending to the top of the wellbore. Upward movement of the mandrel with respect to the body is limitedby engagement of an upwardly facing shoulder 42a on the mandrel with astop ring 47 resting on an upwardly facing shoulder 14b on the body, thestop ring being held in place by a snap ring 49 fitting within acircumferential internal groove 49a in the body. Overlying the head, asuitable guide 48 is secured to the head by cap screws 48a, the upperend of the guide being tapered to facilitate upward passage of thestabilizer past obstructions in the well bore and in the well casing.

The lower portion of the mandrel 39 extends slidably through a bushing50 mounted within the body below a plurality of slots 16, 17 extendingthrough the body, the bushing being held in place by upper and lowersnap rings 50a secured to the body, there being an external seal ring50b on the bushing engaging the body and an internal seal ring 50c onthe bushing slidably and sealingly engaging the periphery of the lowerportion of the mandrel. Stabilizer arms, blades, or ribs 21, 22 aremounted in the body slots 16, 17 for lateral movement between aretracted position, as disclosed in FIG. 1a, and a fully expandedposition, as disclosed in FIG. 3a. The upper portions of these bladesare pivotally mounted on hinge pins 23, 24 extending across the slotsand suitably secured to the body 14. The mandrel also has an expandermember 41a thereon engageable with downwardly and inwardly inclinedinner surfaces 22a on the arms for the purpose of expanding the armsoutwardly when the mandrel 39 moves downwardly within the body 14. Whenthe arms have been expanded outwardly to their maximum extent, asdetermined by engagement of the lower ends 27, 28 of the arms with astop ring 34, 35 suitably secured to the body of the tool below theslots, the outer backing or holding surfaces 41 on the expander aredisposed behind companion surfaces 25, 26 of the arms, to resist inwardmovement of the arms from their fully expanded position (FIG. 3a).

When fully expanded, the outer surfaces 29, 30 of the arms are parallelto the axis of the stabilizer and have an effective diametersubstantially the same as the diameter of the enlarged well bore 300.Downward movement of the mandrel 39 within the body is limited byengagement of its downwardly facing shoulder 42c with a stop ring 42dbearing against an upwardly facing shoulder 46 on the body. Upwardmovement of the mandrel within the body will cause the expander 41a toengage inwardly directed lug portions 22d on the arms for the purpose ofswinging the arms inwardly within the confines of the main body 14 ofthe stabilizer. Bleeder holes 52 extend through the body 14 to vent thespace 51 around the mandrel portion 42 to permit well bore fluid toenter and leave the space and thereby facilitate longitudinal movementof the mandrel with respect to the body 14. The lower mandrel 60includes an upper kelly or drill stem member 62 slidably splined to themain body 63 of the drill bit 15. The exterior 64 of the lower portionof the kelly has a noncircular shape being telescopically received in acorresponding shaped socket 65 in the main bit body. As an example, thekelly exterior 64 and the socket 65 may be of hexagonal shape to anablethe kelly 62 to move longitudinally relative to the main body 63 whilestill transmitting rotary motion and torque to the body.

The mandrel 60 has a limited range of longitudinal movement within thebody 63, downward movement being determined by engagement of the lowerend 66 of the kelly with an inwardly directed body shoulder 67 and itsupward movement being limited by engagement of an external shoulder orpiston portion 68 of the kelly with a cylinder head 69 secured to thebody 63. The upper end of the head has a flange 70 engaging a bodyshoulder 71, the flange being prevented from moving upwardly of the bodyby split snap retainer rings 72 fitting within a body groove 73 andoverlying the flange 70. An annular guide can be releasably secured tothe body 63 by a split snap ring 75 above the retainer rings 72.

The body 63 has a plurality of expansible parts mounted on it. Theseinclude cutter supporting members 76 pivotally mounted in body slots 77on hinge pins 78 suitably secured to the body. Each cutter supportingmember 76 depends from the hinge pin and rotatably carries a toothedroller cutter 79 at its lower end. As shown in FIGS. 1b and 6, thecutter supporting members and the cutters tend to occupy retractedpositions substantially entirely within the confines of the main body 63of the bit. The cutter supporting members 76 and the cutters 79themselves are expandable outwardly, as when the diameter of the wellbore 200 is to be enlarged beyond the inside diameter of the well casing10, 11 through which the drill bit can be lowered and raised. Toaccomplish the expansion, each cutter supporting member has an inclinedexpander surface 80 on its inner portion below the hinge pin 78 whichtapers in an inward and downward direction. Each expander surfaceterminates in a lock surface 81 formed on a lock portion 82 of thecutter supporting member. The outward expansion is accomplished byproducing relative longitudinal movement between the mandrel 60 and thebit body 63, which will produce relative longitudinal movement betweenthe cutter supporting members 76 and the tubular member 83 of themandrel. This tubular member includes a lower portion 84 slidable withina guide bushing 85 mounted within a bridge 86 secured to the body andextending across the body slots 77. This guide bushing 85 is disposedbelow the lock portion 82 of the cutter supporting members.

Located initially substantially above the guide bushing 85 and below thehinge pins 78, and in cutter member recesses 87, is a mandrel lock andexpander 88 which has outer surfaces 89. The lock and expander 88 may beformed integrally with the tubular member 83, the upper end of thelatter being piloted within a socket 90 formed in the lower portion ofthe kelly 62. An enlarged boss 91 on the tubular member engages adownwardly facing shoulder 92 of the kelly, the tubular member 83 beingheld against this shoulder by a suitable spring retainer lock ring 93snapped into an internal groove 94 encompassing the kelly socket 90 andengaging the lower end of the tubular member boss 91.

Drilling mud or other fluid can pass down through the central passage 95in the kelly or drill stem 62 and into the central passage 96 extendingcompletely through the tubular member 83. Leakage of fluid around theexterior of the tubular member 83 is prevented by a suitable side sealring 97 mounted in a peripheral groove 98 in the kelly and engaging theexterior wall of the boss 91.

Assuming that the body 63 of the tool is elevated relatively along thetubular mandrel 60, the inclined expander surfaces 80 of the cuttersupporting members 76 will be shifted upwardly along the lock andexpander portion of the tubular member 83. During such upward shifting,the cutter supporting members 76 and the cutters 79 carried thereby willbe pivoted about the hinge pins 78 and urged in an outward direction.Upward movement of the body 63 with respect to the tubular mandrel 60can continue until the cutters 79 have been shifted outwardly to theirfullest extent, as determined by engagement of the stop shoulders 100 onthe cutter supporting members 76 with companion shoulder 101 formed inthe body on opposite sides of the slots 77. When such engagement occurs,the lower end 66 of the kelly portion of the tubular mandrel will engagethe body shoulder 67 and the lock and expander 88 on the tubular member83 will be disposed behind and in engagement with the lock portions 82on the cutter supporting members 76. (FIGS. 2b, 3b).

The relative longitudinal movement between the tubular mandrel 60 andthe body 63 of the tool is accomplished hydraulically. As shown in thedrawings, the piston or enlarged portion 68 on the drill stem isreceived within a counterbore 102 formed in the upper portion 103 of thebody of the tool, the upper portion actually constituting a cylinderhaving a cylindrical wall extending from a lower shoulder 104, definingthe bottom of the counterbore, to the cylinder head 69. A confinedcylinder space 105 is formed between the piston portion 68 of the kelly,the periphery of the kelly above the piston 68, and the cylinder 103,69. A suitable packing or side seal ring 106 may be disposed in asuitable piston ring groove 107 in the piston 68, which is adapted toslidably seal against the cylindrical wall 104a of the cylinder. Fluidis thereby prevented from passing in a downward direction between thepiston 68 and the cylinder 103. Similarly, fluid is prevented frompassing in an upward direction out of the annular cylinder space 105 byan inner side seal ring 108 carried in an external groove 109 in thecylinder head 69 and slidably and sealingly engaging the periphery ofthe kelly 62 above the piston 68, and also by an outer side seal ring110 disposed in an external groove 111 in the head 69 and sealingengaging the cylinder wall 104a.

Fluid under pressure in the drill bit collar 13 and in the tubularmandrel passage 95 can be fed into the cylinder space 105 through one ormore side ports 112 establishing communication between the centralpassage 95 through the kelly 62 and the cylinder space. Such fluid underpressure is developed, in the form of invention disclosed in thedrawings, by virtue of the fact that the passage 96 through the tubularmember 83 of the mandrel is of a restricted diameter as compared to thepassage 95 of the kelly portion of the mandrel. As a result, the pumpingof drilling mud or other fluid at an adequate rate through the apparatuswill build up a back pressure of fluid in the passage 95, which pressurewill be imposed on the fluid in the cylinder space 105, acting upon thecylinder head 69 to urge the body 63 of the tool in an upward directionwith respect to the tubular mandrel 60, to secure the outward expansionof the cutter supporting members 76 and cutters 79 to their fullestextent, as above described.

In addition to effecting outward expansion of the cutter supportingmembers 76 and the cutters 79 to their fullest extent, the fluid canpass downwardly out of the passage 96 through the tubular member 83 andwill then flow upwardly around the cutters 79, to remove the cuttingsand cool the cutters themselves. The cuttings will be flushed upwardlythrough the annulus between the drill pipe and casing to the top of thehole, for appropriate disposal.

To insure the presence of adequate pressure in the cylinder space 105during the circulation of fluid while the hole enlarging operation isbeing conducted, the flow of fluid through the passage 96 is furtherrestricted by a throttle device in the tubular member itself. As shown,the lower portion of the tubular member 83 has a counterbore 113 toreceive a tubular sleeve 114, preferably made of a hard metal, such astungsten carbide, for the purpose of resisting erosive wear. This sleeve114 can be secured in the lower end of the tubular member 83 in anysuitable manner, as by welding. The passage through the sleeve has asmaller diameter than the passage 96.

The supporting members 76 also have inwardly projecting lugs 22d engagedby a mandrel shoulder 22e for the purpose of mandrel 83 swinging themembers 76 and cutters 79 inwardly within the confines of the body 63when the mandrel is elevated within the body.

During the lowering of the drill bit 15 through fluid in the well bore,pressure is sometimes developed in the mandrel passage 95 that issufficiently high as to tend to elevate the body 63 of the tool alongthe mandrel 62, and thereby elevate the cutter supporting members 76along the mandrel and expander 88, which tends to shift the cutters 79outwardly against the wall of the well casing. Such expansion may resistdownward movement of the cutters 79 in the well casing. In the eventthat a liner (not shown) is disposed in the well casing 10, throughwhich a rotary drill bit must also pass, even a relatively smallexpansion of the cutters 79 might prevent the tool from entering andbeing moved through the liner. Even in the absence of the development ofhydraulic pressures, the body 63 of the tool, or the cutter supportingmembers 76 and cutters 79 are engaging the inner wall of the wellcasing, tending to resist downward movement of the body therewithin. Themandrel 60 then tends to telescope downwardly in the body 63, causingthe expander 88 to engage the expander surfaces 80 on the cuttersupporting members 76 and shift the latter and the cutters 79 outwardly.

Inadvertent outward movement of the cutter supporting members 76 and thecutters 79 themselves is prevented in a positive manner without,however, preventing expansion of the cutter supporting members and thecutters when such expansion is desired.

As shown in FIGS. 1b and 6, a releaseable retainer 120 is secured to theexternal portion of the body 63 of the tool and overlies the outersurface of a cutter supporting member 76. If desired, only one of theretainer members 120 can be provided in the drill bit since any tendencyfor relative longitudinal movement to occur between the mandrel 60 andthe body 63 will cause the mandrel expander 88 to engage the expandersurface 80 on the cutter supporting member 76 held by the retainer andpreclude relative longitudinal movement between the mandrel and thebody. However, if desired, a retainer 120 can be provided for eachcutter supporting member 76. Each retainer member has spring-likecharacteristics up to a certain point, so that even if the relativelongitudinal movement between the mandrel 60 and body 63 does result ina slight outward expansion of the cutter supporting members 76 andcutters 79, the relieving of the expanding force will cause the retainermembers 120 to reshift the cutter supporting members 76 back to theirfull initial retracted position within the body slot 77.

The combination stabilizer and expansible bit apparatus is loweredthrough the well casing 10 on a string of drill pipe 13 with thestabilizer body 14 in a lower position and the bit body 63 in its lowerposition with respect to their respective mandrels, the lugs or fingers22d on the respective arms engaging the mandrel shoulders which willretain such arms in their inward positions, as disclosed in FIGS. 1a and1b. After the bit has been lowered below the casing shoe 11, its cutters79 can be expanded by pumping fluid down through the drill string 13,through the central passage 39c of the stabilizer mandrel 39 and thelower passage 14p of the body into the passage 95, 96 of the bitmandrel, the fluid discharging through the orifice 114, and building upa back pressure in the upper passage 95 of the mandrel, the ports 112,and cylinder 105. Such pressure elevates the body 63, cutter arms 76 andcutters 79 with respect to the mandrel 60 while the apparatus is beingrotated at the proper speed, the cutters swinging outwardly about theirhinge pins and beginning to penetrate the wall of the bore hole 200. Thedrill string and apparatus are not lowered at this time, the cutters 79cutting into the wall of the hole, and as they do so enlarging the hole,the body 63 of the tool progressively moving relatively upwardly alongthe mandrel 60 until the cutters have been expanded outwardly to theirfullest extent, as disclosed in FIGS. 2b and 3b.

Downweight of the drill string 13 can now be imposed on the stabilizermandrel 39 which moves downwardly and causes its expander 41a to engagethe stabilizer arms 21, 22 and swing them outwardly. However, the armscan only swing outwardly to a partial extent, as illustrated in FIG. 2a,the downweight being transmitted through the arms and hinge pins 24 tothe stabilizer body 14, and from the stabilizer body to the bit mandrel60. The lower end of the kelly engages the body shoulder 67 so that thedrilling weight is transferred directly from the body through the hingepins 78 and cutter arms 76 to the cutters 79. Drilling in a downwarddirection proceeds to produce the enlarged hole 300.

When the stabilizer arms 21, 22 reach the enlarged diameter portion ofthe bore hole, they can swing outwardly to their fullest extent, asdisclosed in FIG. 3a, at which time the mandrel shoulder 42c engages thestop ring 42d which, in turn, bears against the body shoulder 46, sothat the drilling weight is thereafter transmitted directly from themandrel 39 to the body 14, and from the body and bit mandrel 60 to thebit body 63, and then to the cutters 79, the parts occupying thepositions illustrated in FIGS. 3a and 3b. The rotation and torque arealso transmitted from the drill string stabilizer mandrel 39 to thestabilizer body 14, and from the stabilizer body to the bit mandrel 60and bit body 63, and then to the supporting arms 76 and cutters 79.

As drilling of the enlarged hole proceeds, the stabilizer arms 21, 22,which are locked in their outward position, with their extendedlongitudinal external surfaces 29, 30 facing the wall of the well borein close adjacency thereto, will maintain the hole enlarging bit 15centered with respect to the axis of the well bore, and thereby preventdeviation of the bit, which would tend to produce a deviated ormisaligned enlarged well bore 300. The outer surfaces 29, 30 of thestabilizer arms 21, 22 can, if desired, be hardfaced or may havehardfaced inserts, such as sintered carbide buttons, or the like,mounted thereon, in a known manner, to increase the resistance to wearof the stabilizer arms.

After the well bore has been drilled to its predetermined extent, thedrill string 13 is elevated, which will elevate the stabilizer mandrel39 within the body 14 and cause the expander 41a to engage the lugs 22don the stabilizer arms to swing them back to their initial retractedposition, as shown in FIG. 1a. Continued upward movement of the drillpipe and stabilizer will cause the bit mandrel 60 to be elevated withinthe bit body 63, its shoulder 22e engaging the lugs 22d on the cuttersupporting members 76 and swinging the cutter supporting members andcutters 79 back to their retracted position, as disclosed in FIG. 1b.When the stabilizer arms are in their fully retracted position, themandrel 39 engages the upper head 47 secured to the body 14; whereas,the bit mandrel 60 will engage the head 69 secured to the bit body 63,the parts then moving as a unit upwardly through the well bore andthrough the well casing to the top of the hole.

When the stabilizer arms 21, 22 are fully expanded, the mandrel 39 andbody 14 are coengaged and function as a unitary body means. Similarly,with the supportive member 76 and cutter 79 fully expanded, the mandrel60 and body 63 are coengaged and function as a unitary body means. Inturn, both body means are rigidly associated with each other foroperation as a single unit.

We claim:
 1. A stabilized rotary well drilling bit apparatus; comprisingrotatable body means connectable to a drilling string, initiallyretracted, outwardly expandable cutter means mounted on said body meansfor rotation therewith and for enlarging the diameter of a bore hole toa predetermined extent, initially retracted outwardly expandablestabilizer means trailing said cutter means and mounted on said bodymeans for rotation therewith together with said cutter means, means foreffecting joint rotation of said body means, cutter means and stabilizermeans during drilling of the enlarged bore hole, means for expandingsaid cutter means laterally outwardly to enlarge the bore hole to saidpredetermined extent, and means for expanding said stabilizer meanslaterally outwardly to a position closely adjacent the wall of theenlarged bore hole.
 2. Apparatus as defined in claim 1; and means forlimiting the extent of outward expansion of said stabilizer means. 3.Apparatus as defined in claim 2; and means for limiting the extent ofoutward expansion of said cutter means.
 4. Apparatus as defined in claim1; means mounting said stabilizer means for pivotal movement relative tosaid body means between retracted and expanded positions.
 5. Apparatusas defined in claim 4; and means for limiting the extent of outwardexpansion of said stabilizer means.
 6. Apparatus as defined in claim 5;and means for limiting the extent of outward expansion of said cuttermeans.
 7. Apparatus as defined in claim 1; said body means including anupper body on which said stabilizer means are mounted, said means forexpanding said stabilizer means including an upper mandrel shiftablealong said upper body; said body means further including a lower body onwhich said cutter means are mounted, said means for expanding saidcutter means including a lower mandrel shiftable along said lower body.8. Apparatus as defined in claim 7; and means for limiting the extent ofoutward expansion of said stabilizer means.
 9. Apparatus as defined inclaim 8; and means for limiting the extent of outward expansion of saidcutter means.
 10. Apparatus as defined in claim 7; means mounting saidstabilizer means for pivotal movement on said upper body betweenretracted and expanded positions; and means mounting said cutter meansfor pivotal movement on said lower body between retracted and expandedposition.
 11. Apparatus as defined in claim 10; and means for limitingthe extent of outward expansion of said stabilizer means.
 12. Apparatusas defined in claim 11; and means for limiting the extent of outwardexpansion of said cutter means.
 13. A stabilized rotary well drillingbit apparatus; comprising body means connectable to a drilling string:outwardly expandable cutter means mounted on said body means forenlarging the diameter of a bore hole; outwardly expandable stabilizermeans positioned above said cutter means and mounted on said body means;means for expanding said cutter means laterally outwardly; and means forexpanding said stabilizer means laterally outwardly to a positionadjacent the wall of the enlarged bore hole; said body means includingan upper body on which said stabilizer means are mounted, said means forexpanding said stabilizer means including an upper mandrel shiftablealong said upper body; said body means further including a lower body onwhich said cutter means are mounted, said means for expanding saidcutter means including a lower mandrel shiftable along said lower body;means connecting said lower mandrel to said upper body, said uppermandrel having means thereon adapted for connection to a drill string.14. Apparatus as defined in claim 10; and means connecting said lowermandrel to said upper body, said upper mandrel having means thereonadapted for connection to a drill string.
 15. Apparatus as defined inclaim 1; said stabilizer means comprising arms pivotally mounted on saidbody means; and means for limiting the extent of outward expansion ofsaid arms.
 16. Apparatus as defined in claim 15; said body meansincluding an upper body on which said arms are mounted; said means forexpanding said arms including an upper mandrel shiftable along saidupper body, said body means further including a lower body on which saidcutter means are mounted, said means for expanding said cutter meansincluding a lower mandrel shiftable along said lower body.
 17. Apparatusas defined in claim 16; means connecting said lower mandrel to saidupper body, said upper mandrel having means thereon adapted forconnection to a drill string.
 18. A stabilizer for use in a bore hole,comprising a body, stabilizer members pivotally mounted on said bodyabout axes transverse to the axis of said body for rotation therewithand for shifting between retracted and expanded positions, means forexpanding said members laterally outwardly of said body for engagementwith the wall of the bore hole, means for limiting the extent of outwardexpansion of said members, the outer surfaces of said stabilizer membersbeing elongate and substantially parallel to the axis of said body whensaid members are fully expanded outwardly of said body, said outersurfaces being arcuate and of uninterrupted extent to enable saidmembers to slide circumferentially around the wall of the bore hole whensaid members are in their fully expanded position.
 19. A stabilizer asdefined in claim 18; said expanding means including a mandrel shiftablealong said body.
 20. Apparatus as defined in claim 19; said mandrelhaving means thereon for connection to a drill string.